The present invention relates to life safety devices having a battery assembly with a rechargeable battery.
Flush mount life safety devices are used in residential and commercial buildings to provide warning to occupants of hazards such as fire or a buildup of unsafe gases such as carbon monoxide. The life safety devices are typically mounted on a wall or a ceiling of a building. Typically, flush mount life safety devices are powered by a battery assembly that includes a rechargeable battery. The life safety device is connected to a source of AC power, which provides electrical current for charging the rechargeable battery.
The rechargeable battery is a part of a battery assembly that is mounted in the life safety device at the factory. Once the battery assembly is connected to the circuitry of the life safety device, power can be drawn from the battery prior to the device being placed into service. Under those conditions, the life safety device is not connected to a source of AC power, and therefore the battery is not being recharged.
The battery assembly typically includes a rechargeable battery, a battery charging circuit, a booster circuit to increase the battery voltage to a voltage level required to operate the life safety device circuitry, and a battery protection circuit. The battery protection circuit provides over-current protection, which disconnects the battery if the current draw is too high, and over-discharge protection to prevent the battery cell voltage from decreasing to a level which will cause internal damage to the cell.
When shipping a life safety device with a rechargeable battery, it has been a conventional method to place the battery protection circuit in an over-current protection mode. This may be achieved, for example, by shorting the battery voltage terminal of the battery assembly to the ground terminal prior to shipping the product.
To ensure the long service life for the life safety device (e.g., a ten year service life), the shelf life of the device must be limited. The shelf life is determined by the current consumption required between the time of installation of the battery assembly in the device and the installation of the device with a connection to AC power. If the product is kept “on the shelf” (i.e., either unsold or sold but not yet installed) beyond the shelf life, the battery cell voltage may slowly fall to a level that causes internal damage to the cell(s) of the battery. To avoid cell damage, any device that has exceeded its shelf life has to be returned to the factory, the battery must be replaced with a newly recharged battery, and the product must be repackaged and reshipped.
Although the over-current protection reduces the amount of current drawn from the battery prior to installation, the limited shelf of the devices life has remained an issue. Removal of products from stores because of expired shelf life of the battery assembly is inconvenient and expensive.